1. Field of the Invention
The present invention is directed to an active matrix liquid crystal display (AMLCD) and a method for driving thereof, and more particularly, to an AMLCD incorporating pixel inversion with reduced drive pulse amplitudes.
2. Discussion of the Prior Art
FIG. 1 illustrates a conventional AMLCD circuit 10 such as described in U.S. Pat. No. 5,790,090 directed to a bootstrapped pixel method permitting the use of lower-voltage data drivers and low drive pulse amplitudes.
In the AMLCD device of FIG. 1, a display 1 comprising pixel assemblies 14 is arranged in a matrix of rows 12 labeled A, . . . ,D . . . , and columns 13. Each pixel assembly 14 includes a display element 5 having a display electrode 5A, and a semiconductor device, e.g., a metal-oxide-semiconductor field effect transistor or a thin-film transistor (TFT), Q, having a control port 3, an input port 2, and an output port 4. Each of the output ports is connected to a corresponding display electrode 5A. A plurality of bootstrap 11, gate, and data lines are provided, with each bootstrap line 11 connected, e.g., capacitively connected, via capacitor 7, to the display electrodes 5A of two rows (by way of example) of pixel assemblies. Each gate line is connected to the control ports 3 arranged in one of the rows. In addition, each data line is connected to the input ports 2 arranged in one of the column. Sharing bootstrap lines between two or more rows reduces the number of bootstrap lines to half, or less than half, the number of gate lines. Each bootstrap line is connected to a bootstrap pulse timing and generating circuit to provide a bootstrap pulse that shifts voltages on the pixel or display electrodes 5 in only one direction, e.g. in the positive direction, relative to a common electrode 6. The bootstrap pulse drive method as described in U.S. Pat. No. 5,790,090, enables operation of AMLCD reflective projection light valves implementing narrow line-width MOS technologies with reduced data line voltage and the gate line voltages, in addition to a low pixel voltage and a fixed common electrode voltage.
The method of frame inversion in pixel displays involves applying signal voltages to each pixel of the array of the same polarity relative to the common electrode voltage during each frame, and inverting the polarity each new frame. This method is desirable with small pixels because it minimizes visual artifacts due to crystalline disclination, but it is vulnerable to flicker and crosstalk. In pixel inversion, the polarity is inverted by pixel in each row, by row and by frame. Pixel inversion is generally regarded as best with respect to flicker and crosstalk. Inversion by either row or column as well as by frame are approximately equivalent and intermediate in performance between frame and pixel inversion.
It is thus highly desirable to incorporate a pixel inversion scheme in the bootstrapped pixel method of the AMLCD device shown in FIG. 1.